Enter the text here that is the new abstract information for your application. This section must be no E 0 longer than 30 lines of text. The key to understanding the results of the STEP/Phambili trials is first to model the results of the trial in controlled experiments using mucosal SIV inoculation of rhesus macaques. Thus, we will determine the effectiveness and potential of the Merck trivalent HIV adenovirus 5 vector vaccine (V520) for enhancing susceptibility to S1V in a rhesus macaque model of mucosal HIV transmission. If models of vaccine protection or enhancement are established, the immune mechanisms and inflammation/activation associated with any protective or enhancing effects can be defined in a renewal application. 0'Qvic' am- .,c vii